1. Field of the Invention
The present invention relates to adjustable tables, more particularly, tables having a work surface that can carry heavy objects and yet be adjusted into multiple elevational positions. Even more particularly, the present invention relates to an improved height adjustable table having a spring counterbalance that enables easy height adjustment, and a load balance indicator that indicates to a user if the spring is over wound, or if too much weight is placed on the table, even when supporting weighted objects such as computers, monitors and the like.
2. General Background of the Invention
Adjustable tables have been in use for many years. There are several adjustable height tables that are commercially available. Several of these adjustable height tables were patented as drafting tables. Some were sold under the trademark Hamilton. For example, U.S. Pat. 3,273,517 issued to Amthor, entitled "Drafting Table" and assigned to Hamilton Mfg. Co., discloses a table having elevating sides that raise and lower a work surface and wherein a counterbalanced spring (see FIG. 11) can be adjusted to compensate for different loads such as various weights of the drafting board and the objects mounted thereon. U.S. Pat. 3,273,517 is incorporated herein by reference.
U.S. Pat. 3,638,584 shows an adjustable height table that purports to be a drafting table construction.
An example of a height adjustable table is shown in the Winchell U.S. Patent 5,408,940. In the Winchell patent, a work table is cantilevered from posts supported for vertical motion inside columns from a base. A drive connected between the work table and the base changes the height of the work table and is located between the columns and posts. Each post carries a rack that engages with a pinion supported by a column for rotation about a common axis. A rigid shaft interconnects two pinions and prevents relative pinion rotation. A stabilizing structure in each column interacts with the post to maintain engagement between the rack and pinion structure and maintains the work table in a horizontal position during adjustment and use.
U.S. Pat. No. 5,289,782 issued to John Rizzi et al. discloses an adjustable height table having a top that can be vertically adjusted to various heights by a pair of telescoping legs and a counter-balanced weight mechanism which includes a weight box and weights that can be easily added or removed by the user depending on the weight carried by the table top. A locking mechanism includes a spring urged threaded half nut and a stationary threaded rod that enables the table top to be locked in place one a desired height is achieved.
An improved load compensator for a spring counter weighting mechanism is disclosed in U.S. Pat. 5,400,721. In the '721 patent, a small cam provides a constant counterweight force. The cam provides a constant torque to a drum on which are wound cables for exerting a constant counter weighting force. A manually operable device for altering the relative radial positions of the cam and drum varies the mount of the constant counter weighting force. The cam is rotated with respect to the drum by a spur gear fitted within a ring gear fixed to the drum and rotated by a knob connected to an axle carrying a pinion gear engaging the spur gear. The spiral surface can be effectively reconfigured with respect to a portion of the cable fitting there around.
Other examples of adjustable height tables include U.S. Pat. Nos. 544,836; 2,982,050; 2,982,050; 3,213,809; 3,364,881; 3,908,560; 4,130,069; 4,619,208; 4,751,884; 5,322,025; and 5,339,750.
A release mechanism is provided for enabling a user to disengage a locking mechanism that holds the work platform in a particular position. The release mechanism slowly lowers the table if it is overloaded with too much weight. In a situation where the counter balance spring has been over wound, the release mechanism includes a brake that slowly elevates the table gradually releasing the energy stored in the counter balanced spring.
The present invention provides an improved adjustable height table with improved brake mechanism for safely and easily indicating to a user when it is overloaded with wright or when its counter balance spring has been over wound.
One of the primary uses for adjustable height tables is the support of a heavy object such as a computer and/or monitor at a comfortable elevation for the user. Because computers and monitors are relatively heavy, a problem exists when the table position is to be changed to a higher or lower elevational position, such as when the user chooses to stand or to sit. In such a situation, adjustable height tables can drop too quickly The weighted table top of the table can cause injury if it is loaded with a heavy object such as a monitor, computer or the like and the user adjusts without proper counterbalance.